Binding agents are typically mixed with fibers and pieces of material to hold the fibers together and to impart mechanical strength to the resultant fiber mixture. Conventional binding agents include various types of resins, glues and gums.
For many applications, it is desirable to use binding agents that strengthen the mixture without significantly changing its other properties, such as absorbency. Moreover, it is often desirable to employ binding agents that provide mechanical strength irrespective of whether the fiber mixture is in a wet or a dry state or changes between those two states.
Various types of polysaccharides have been used as thickeners, fillers, and the like for various applications. Microbially produced cellulose, including cellulose produced by competent strains of Acetobacter, has been adapted for use in a variety of applications.
Japanese Kokai Patent No. Sho 61(1986)-113601 discloses macerated cellulose substances and methods for manufacturing such substances. Cellulose produced by microorganisms, e.g. Acetobacter, having the structure of ribbon-format microfibrils entangled in a complex form, is macerated using mechanical shear force. Industrial applications for the macerated cellulose product include viscosifiers for cosmetic products or coating materials, strengthening food raw material bases, retaining water, improving food stability, as low calorie additives or emulsification stabilizing agents, as a reinforcer for polymers, especially aqueous-system polymers, and for use in a paper or solid form.
European Patent Application Publication No. 0 212 289 teaches absorbent, retentive cellulose pulp. Cellulose is microfibrillated, then frozen, subjected to solvent exchange, and treated with a crosslinking agent. The product exhibits increased absorption, fluid retention, and high wet resiliency, even after having been highly compressed. Applications include use in napkins, tampons, etc. to increase to total absorption capacity and wicking rate. European Patent Application Publication No. 0 209 884 is commonly assigned and also teaches freeze-dried, cross-linked microfibrillated cellulose for use in absorbent products.
U.S. Pat. No. 4,374,702 teaches microfibrillated celluloses (MFC) having properties different from previously known celluloses, but not substantially chemically changed from the cellulose starting material. The U.S. Pat. No. '702 patent teaches that MFC is suitable for use with paper products and non-woven sheets made, for example, using Rayon, to improve their strength. The results are said to establish that MFC is valuable as a binder for paper and other materials having non-woven constructions.
Japanese Kokai Patent No. Sho 61(1986)-221201 teaches a method of manufacturing fine cellulose crystals wherein microbially produced cellulose is suspended in one or more media selected form an acid stronger than 1N, a base stronger than 1N, a polar solvent and an ammoniacal solution of a metal oxide, and mechanically ground before or after drying. The cellulose substance is in the form of tangled ribbon-shaped microfibrils and is in a gel state. Fine cellulose crystals obtained using this method are about 0.01 to 0.1.mu. in size. They are used in food additives, as agents in drugs, cosmetics and paint, in additives, in binders, in high strength composite materials, and as a support material for chromatography. Japanese Kokai Patent No. Sho 61(1986)-215635 teaches fine cellulose crystals prepared in accordance with the methods disclosed in the previous reference. The fine cellulose powder may be used as a bonding agent by applying a suspension of it between boards.
European Patent Application No. 0 243 151 teaches a microbially-produced cellulose gel modified by physical or chemical bonding with an animal cell adhesive protein, and/or by substituting the hydrogen of at least some hydroxyl groups with a positively or negatively charged organic group. The gel is useful as a carrier for mass culture of animal cells or as a medical vulnerary cover (i.e. artificial skin). The gel may be dried and returned to a gel state. Included as auxiliary materials to be complexed are non-woven fabrics and other fabrics composed of natural fibers or man-made fibers, films, paper sheets and porous films, organic or inorganic granules of alumina, glass and crystalline celluloses, and other materials. The system to be complexed may be incorporated in the culture media and the cellulose formed directly on or in the substance, or the gel may be impregnated or backed with the substance to be complexed, or the gel may be disintegrated and then complexed with the substance.
Japanese Kokai Patent No. Sho 61(1986)-212295 teaches methods of manufacturing bacterial cellulose in cultures of inositol or phytic acid. The cellulosic materials are edible and having application in the food industries, in maintaining the viscosity of food, cosmetics, and paints, and for food-base reinforcements, water retention, stability enhancement, low calorie additives, and emulsion-stabilization aids. Degradation products of cellulosic materials having microfibrillar structures are used for paper-like or solid products and in various industrial materials because of their high tensile modulus.
PCT Publication No. WO 89/11783 teaches applications for microbial cellulose including in situ application to restore and protect paper documents, especially fragile, acid-damaged documents, microchips, electronic components, circuit boards, and archeological artifacts. Use of microbial cellulose in the manufacture of latex items, such as condoms, and in the preparation of currency and other types of paper is also disclosed.
PCT Publication No. WO 89/12107 teaches specialty products utilizing microbial cellulose, including: non-wovens and films, specialty papers, filtration and separation media such as membranes; specialty carriers for battery fluid and fuel cells; coating metals on bacterial cellulose to produce materials having special electronic properties; carriers for foods, cosmetics, skin/hair treating materials and internal drugs; mixing agents and viscosity modifiers for surface coatings, paints, fillers, plasters, glues, adhesives, grouts and caulks; specialty fillers such as carbonized fillers for use as polymer fillers; light transmitting optical fibers; wavelength and other electromagnetic and radiation modifying materials; microfiller blends, especially with melt-blown and other polyolefin fillers; substrate, e.g. culture media; foods, food substrates and fiber substitutes; specialty laboratory uses; specialty lint-free clothing; synthetic leather and other textured and special appearance surfaces; diet fiber substitutes; blends with other fibers such as cotton, polyesters and nylons in woven and non-woven fabrics; and moisture-absorbing, soil-enhancing additives and conditioners. Bacterial cellulose was also used to promote seedling and spore germination. This publication teaches that microbial cellulose pellicles and other variants are useful as gums and gels for a wide variety of applications.
A. F. Turbak, et al., in "Microfibrillated Cellulose, A New Cellulose Product: Properties, Uses and Commercial Potential", Journal of Applied Polymer Science: Applied Polymer Symposium 37:815 (1983), teach preparation of microfibrillated cellulose (MFC) and applications for MFC as thickeners to yield viscous mixtures that exhibit thixotropic properties and suspend solid particles. Applications include: food products; cosmetics; paints; paper and non-woven textiles; oil field services; and medical carriers and barriers.
H. Yokota, et al., in "Microfibrillated Substances and Their application for Cellulose, Chitin and Chitosan, "1987 International Dissolving Pulps Conference/TAPP1 Proceedings, teaches preparation of microfibrillated substances, and viscosity and water retention values for the prepared product. Applications include binders for high performance paper, including inorganic papers and dietary fibers.
As is illustrated by the references described above, it is known to use various types of cellulose, including microbially produced cellulose, in a variety of applications. Cellulosic material is typically used to bind or strengthen woven or non-woven fibrous materials, fine particulate materials, or to confer enhanced rheological properties to various suspensions. To the inventors' knowledge, microbially produced cellulose has not been used in applications involving larger fragments of material, such as biomass fragments, relatively large particulate materials, or the like.
Hydraulic mulches comprise relatively large fragments of particles of material, such as biomass fragments, that are mixed with water to form a slurry. Binding agents are typically added to hydraulic mulch slurries to provide enhanced structural integrity upon application of the mulch. The slurry is sprayed onto the ground, effectively inhibiting soil erosion. Seeds may additionally be incorporated in the slurry, in which case the mulch protects the seeds and soil from adverse weather conditions and retains moisture to promote germination. Fertilizers and other plant growth and soil stabilization aids may also be included in hydraulic mulches.
Binding agents employed in mulches are commonly referred to as "tackifiers", with the hydraulic mulch product containing tackifier being referred to herein as the tackified hydraulic mulch. Guar gum is conventionally used as a tackifier, but it has a number of disadvantages. For instance, guar gum, which is generally used in the form of a finely ground powder, is difficult to disperse through a hydraulic mulch slurry to produce a uniformly tackified hydraulic mulch. In this regard, conventional hydraulic mulching equipment lacks the power necessary for generating the significant shear forces required to provide adequate premixing of the gum and hydraulic mulch. The tackifier/binding agent component of the tackified hydraulic mulch enhances the strength and integrity of a mat-like tackified mulch structure and may assist in adhering the mat-like mulch structure to the surface upon which it is applied. Consequently, non-uniformly tackified hydraulic mulches may exhibit reduced structural integrity and reduced adherent ability, which may result in partial removal of the mulch components from the surface upon which they are applied by wind, rain, etc.
Binding agents that maintain the strength and integrity of the mixture despite changes in the moisture content of the material are desirable in many applications, including the tackified hydraulic mulch application described above. Other such applications include numerous paper products, such as paper towels, wipes, tissues, or the like, which generally comprise natural or treated fibrous material. These products (hereafter collectively referred to as "fibrous products") may comprise natural wood pulp fibers, or wood pulp fibers which have been chemically and/or physically treated to impart desired properties. For example, wood pulp fibers may be treated to increase the absorbency of the product. It can be appreciated that binding agents used in the manufacture of fibrous products will be especially advantageous if they provide strength despite changes in the moisture content of the fibrous product.